Hyperpolarized [1-13 C]pyruvate combined with the hyperinsulinaemic euglycaemic and hypoglycaemic clamp technique in skeletal muscle in a large animal model

New Findings

What is the central question of this study?

Is it possible to combine the hyperpolarized magnetic resonance technique and the hyperinsulinaemic clamp method in order to evaluate skeletal muscle metabolism in a large animal model?

What is the main finding and its importance?

The logistical set‐up is possible, and we found substantial increments in glucose infusion rates representing skeletal muscle glucose uptake but no differences in ratios of [1‐¹³C]lactate to [1‐¹³C]pyruvate, [1‐¹³C]alanine to [1‐¹³C]pyruvate, and ¹³C‐bicarbonate to [1‐¹³C]pyruvate, implying that the hyperpolarization technique might not be optimal for detecting effects of insulin in skeletal muscle of anaesthetized animals, which is of significance for future studies.

Abstract

In skeletal muscle, glucose metabolism is tightly regulated by the reciprocal relationship between insulin and adrenaline, with pyruvate being at the intersection of both pathways. Hyperpolarized magnetic resonance (hMR) is a new approach to gain insights into these pathways, and human trials involving hMR and skeletal muscle metabolism are imminent. We aimed to combine the hyperinsulinaemic clamp technique and hMR in a large animal model resembling human physiology. Fifteen anaesthetized pigs were randomized to saline (control group), hyperinsulinaemic euglycaemic clamp technique (HE group) or hyperinsulinaemic hypoglycaemic clamp technique (HH group). Skeletal muscle metabolism was evaluated by hyperpolarized [1‐¹³C]pyruvate injection and hMR at baseline and after intervention. The glucose infusion rate per kilogram increased by a statistically significant amount in the HE and HH groups (P < 0.001). Hyperpolarized magnetic resonance showed no statistically significant changes in metabolite ratios: [1‐¹³C]lactate to [1‐¹³C]pyruvate in the HH group versus control group (P = 0.19); and ¹³C‐bicarbonate to [1‐¹³C]pyruvate ratio in the HE group versus the control group (P = 0.12). We found evidence of profound increments in glucose infusion rates representing skeletal muscle glucose uptake, but interestingly, no signs of significant changes in aerobic and anaerobic metabolism using hMR. These results imply that hyperpolarized [1‐¹³C]pyruvate might not be optimally suited to detect effects of insulin in anaesthetized resting skeletal muscle, which is of significance for future studies.

Remodeling after myocardial infarction and effects of heart failure treatment investigated by hyperpolarized [1-13 C]pyruvate magnetic resonance spectroscopy

PURPOSE

Hyperpolarized [1-¹³ C]pyruvate MRS can measure cardiac metabolism in vivo. We investigated whether [1-¹³ C]pyruvate MRS could predict left ventricular remodeling following myocardial infarction (MI), long-term left ventricular effects of heart failure medication, and could identify responders to treatment.

METHODS

Thirty-five rats were scanned with hyperpolarized [1-¹³ C]pyruvate MRS 3 days after MI or sham surgery. The animals were re-examined after 30 days of therapy with β-blockers and ACE-inhibitors (active group, n = 12), placebo treatment (placebo group, n = 13) or no treatment (sham group, n = 10). Furthermore, heart tissue mitochondrial respiratory capacity was assessed by high-resolution respirometry. Metabolic results were compared between groups, over time and correlated to functional MR data at each time point.

RESULTS

At 30 ± 0.5 days post MI, left ventricular ejection fraction (LVEF) differed between groups (sham, 77% ± 1%; placebo, 52% ± 3%; active, 63% ± 2%, P < .001). Cardiac metabolism, measured by both hyperpolarized [1-¹³ C]pyruvate MRS and respirometry, neither differed between groups nor between baseline and follow-up. Three days post MI, low bicarbonate + CO₂ /pyruvate ratio was associated with low LVEF. At follow-up, in the active group, a poor recovery of LVEF was associated with high bicarbonate + CO₂ /pyruvate ratio, as measured by hyperpolarized MRS.

CONCLUSION

In a rat model of moderate heart failure, medical treatment improved function, but did not on average influence [1-¹³ C]pyruvate flux as measured by MRS; however, responders to heart failure medication had reduced capacity for carbohydrate metabolism.

Sex Differences in Kidney Function and Metabolism Assessed Using Hyperpolarized [1-13C]Pyruvate Interleaved Spectroscopy and Nonspecific Imaging

Metabolic sex differences have recently been shown to be particularly important in tailoring treatment strategies. Sex has a major effect on fat turnover rates and plasma lipid delivery in the body. Differences in kidney structure and transporters between male and female animals have been found. Here we investigated sex-specific renal pyruvate metabolic flux and whole-kidney functional status in age-matched healthy Wistar rats. Blood oxygenation level–dependent and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) were used to assess functional status. Hyperpolarized [1-¹³C]pyruvate was used to assess the metabolic differences between male and female rats. Female rats had a 41% ± 3% and 41% ± 5% lower absolute body and kidney weight, respectively, than age-matched male rats. No difference was seen between age-matched male and female rats in the kidney-to-body weight ratio. A 56% ± 11% lower lactate production per mL/100 mL/min was found in female rats than in age-matched male rats measured by hyperpolarized magnetic resonance and DCE MRI. Female rats had a 33% ± 11% higher glomerular filtration rate than age-matched male rats measured by DCE MRI. A similar renal oxygen tension (T2*) was found between age-matched male and female rats as shown by blood oxygenation level–dependent MRI. The results were largely independent of the pyruvate volume and the difference in body weight. This study shows an existing metabolic difference between kidneys in age-matched male and female rats, which indicates that sex differences need to be considered when performing animal experiments.

Autologous cartilage and fibrin sealant may be superior to conventional fat grafting in preventing physeal bone bridge formation - a pilot study in porcines

PURPOSE

The article compares physeal recovery after insertion of autologous cartilage and a conventional fat graft in a standardized porcine physeal gap model. Presence of a bone bridge was the primary outcome.

METHODS

Ten porcines in two groups of five were included in a paired design. A standardized physeal gap in the distal femur was made in all animals. One group (n = 5) was randomized for deposition of autologous cartilage and a Tisseel^® or Tisseel^® alone. The autologous cartilage was harvested from the femoral articular surface. The other group was randomized for fat grafting or no grafts at all. All animals were housed for 14 weeks. Magnetic resonance imaging (MRI) was performed at 14 weeks prior to euthanasia. The physis was harvested for histology.

RESULTS

MRI - Three bone bridges were seen in the fat grafted gaps. All empty gaps formed a bone bridge. No gaps filled with autologous cartilage and Tisseel^® resulted in bone bridges. One gap filled with Tisseel^® only caused a bone bridge. Histology - The cartilage grafted gaps recovered with physeal-like cartilaginous tissue in histological analysis.

CONCLUSIONS

Fat grafts seems ineffective in preventing bone bridges. The use of autologous cartilage may be superior to the current treatment. However, donor site complications were not investigated. The study serves as a proof of concept study and requires further investigation.

LEVEL OF EVIDENCE

III.

Redundancy in regulation of lipid accumulation in skeletal muscle during prolonged fasting in obese men

Fasting in human subjects shifts skeletal muscle metabolism toward lipid utilization and accumulation, including intramyocellular lipid (IMCL) deposition. Growth hormone (GH) secretion amplifies during fasting and promotes lipolysis and lipid oxidation, but it is unknown to which degree lipid deposition and metabolism in skeletal muscle during fasting depends on GH action. To test this, we studied nine obese but otherwise healthy men thrice: (a) in the postabsorptive state (“CTRL”), (b) during 72‐hr fasting (“FAST”), and (c) during 72‐hr fasting and treatment with a GH antagonist (GHA) (“FAST + GHA”). IMCL was assessed by magnetic resonance spectroscopy (MRS) and blood samples were drawn for plasma metabolomics assessment while muscle biopsies were obtained for measurements of regulators of substrate metabolism. Prolonged fasting was associated with elevated GH levels and a pronounced GHA‐independent increase in circulating medium‐ and long‐chain fatty acids, glycerol, and ketone bodies indicating increased supply of lipid intermediates to skeletal muscle. Additionally, fasting was associated with a release of short‐, medium‐, and long‐chain acylcarnitines to the circulation from an increased β‐oxidation. This was consistent with a ≈55%–60% decrease in pyruvate dehydrogenase (PDHa) activity. Opposite, IMCL content increased ≈75% with prolonged fasting without an effect of GHA. We suggest that prolonged fasting increases lipid uptake in skeletal muscle and saturates lipid oxidation, both favoring IMCL deposition. This occurs without a detectable effect of GHA on skeletal muscle lipid metabolism.

Nicotinamide riboside does not alter mitochondrial respiration, content or morphology in skeletal muscle from obese and insulin-resistant men

KEY POINTS

This is the first long-term human clinical trial to report on effects of nicotinamide riboside (NR) on skeletal muscle mitochondrial function, content and morphology. NR supplementation decreases nicotinamide phosphoribosyltransferase (NAMPT) protein abundance in skeletal muscle. NR supplementation does not affect NAD metabolite concentrations in skeletal muscle. Respiration, distribution and quantity of muscle mitochondria are unaffected by NR. NAMPT in skeletal muscle correlates positively with oxidative phosphorylation Complex I, sirtuin 3 and succinate dehydrogenase.

ABSTRACT

Preclinical evidence suggests that the nicotinamide adenine dinucleotide (NAD⁺ ) precursor nicotinamide riboside (NR) boosts NAD⁺ levels and improves diseases associated with mitochondrial dysfunction. We aimed to determine if dietary NR supplementation in middle-aged, obese, insulin-resistant men affects mitochondrial respiration, content and morphology in skeletal muscle. In a randomized, placebo-controlled clinical trial, 40 participants received 1000 mg NR or placebo twice daily for 12 weeks. Skeletal muscle biopsies were collected before and after the intervention. Mitochondrial respiratory capacity was determined by high-resolution respirometry on single muscle fibres. Protein abundance and mRNA expression were measured by Western blot and quantitative PCR analyses, respectively, and in a subset of the participants (placebo n = 8; NR n = 8) we quantified mitochondrial fractional area and mitochondrial morphology by laser scanning confocal microscopy. Protein levels of nicotinamide phosphoribosyltransferase (NAMPT), an essential NAD⁺ biosynthetic enzyme in skeletal muscle, decreased by 14% with NR. However, steady-state NAD⁺ levels as well as gene expression and protein abundance of other NAD⁺ biosynthetic enzymes remained unchanged. Neither respiratory capacity of skeletal muscle mitochondria nor abundance of mitochondrial associated proteins were affected by NR. Moreover, no changes in mitochondrial fractional area or network morphology were observed. Our data do not support the hypothesis that dietary NR supplementation has significant impact on skeletal muscle mitochondria in obese and insulin-resistant men. Future studies on the effects of NR on human skeletal muscle may include both sexes and potentially provide comparisons between young and older people.

Assessment of mouse liver [1-13C]pyruvate metabolism by dynamic hyperpolarized MRS

Hyperpolarized [1-13C]pyruvate magnetic resonance (MR) spectroscopy has the unique ability to detect real-time metabolic changes in vivo owing to its high sensitivity compared with thermal MR and high specificity compared with other metabolic imaging methods. The aim of this study was to explore the potential of hyperpolarized MR spectroscopy for quantification of liver pyruvate metabolism during a hyperinsulinemic-isoglycemic clamp in mice. Hyperpolarized [1-13C]pyruvate was used for in vivo MR spectroscopy of liver pyruvate metabolism in mice. Mice were divided into two groups: (i) non-stimulated 5-h fasted mice and (ii) hyperinsulinemic-isoglycemic clamped mice. During clamp conditions, insulin and donor blood were administered at a constant rate, whereas glucose was infused to maintain isoglycemia. When steady state was reached, insulin-stimulated mice were rapidly infused with hyperpolarized [1-13C]pyruvate for real-time tracking of the dynamic distribution of metabolic derivatives from pyruvate, such as [1-13C]lactate, [1-13C]alanine and [13C]bicarbonate. Isotopomer analysis of plasma glucose confirmed 13C-incorporation from [1-13C]pyruvate into glucose was increased in fasted mice compared with insulin-stimulated mice, demonstrating an increased gluconeogenesis in fasted mice. The AUC ratios for [1-13C]alanine/[1-13C]pyruvate (38.2%), [1-13C]lactate/[1-13C]pyruvate (41.8%) and [13C]bicarbonate/[1-13C]pyruvate (169%) all increased significantly during insulin stimulation. Hyperpolarized [1-13C]pyruvate can be used for in vivo MR spectroscopy of liver pyruvate metabolism during hyperinsulinemic-isoglycemic clamp conditions. Under these conditions, insulin decreased gluconeogenesis and increased [1-13C]alanine, [1-13C]lactate and [13C]bicarbonate after a [1-13C]pyruvate bolus. This application of in vivo spectroscopy has the potential to identify impairments in specific metabolic pathways in the liver associated with obesity, insulin resistance and nonalcoholic fatty liver disease.

Influence of Oral Contraceptive Use on Adaptations to Resistance Training

Introduction: The majority of young women use oral contraceptives (OCs). Use of OCs has been associated with lower myofibrillar protein and tendon collagen synthesis rates, but it is unknown whether OCs will limit the adaptive response of myotendinous tissue to resistance training.

Design and Methods: Fourteen healthy untrained young regular OC users (24 ± 1 years, fat% 32 ± 1, 35 ± 2 ml⋅min^-1⋅kg^-1) and 14 NOC users (non-OC, controls) (24 ± 1 years, fat% 32 ± 2, 34 ± 2 ml⋅min^-1⋅kg^-1) performed a 10-week supervised lower extremity progressive resistance training program. Before and after the intervention biopsies from the vastus lateralis muscle and the patellar tendon were obtained. Muscle (quadriceps) and tendon cross-sectional area (CSA) was determined by magnetic resonance imaging (MRI) scans, and muscle fiber CSA was determined by histochemistry. Maximal isometric knee extension strength was assessed by dynamometry while 1 repetition maximum (RM) was determined during knee extension.

Results: Training enhanced CSA in both muscle (p < 0.001) and tendon (p < 0.01). A trend toward a greater increase in muscle CSA was observed for OC (11%) compared to NOC (8%) (interaction p = 0.06). Analysis of mean muscle fiber type CSA showed a trend toward an increase in type II muscle fiber area in both groups (p = 0.11, interaction p = 0.98), whereas type I muscle fiber CSA increased in the OC group (n = 9, 3821 ± 197 to 4490 ± 313 mm², p < 0.05), but not in NOC (n = 7, 4020 ± 348 to 3777 ± 354 mm², p = 0.40) (interaction p < 0.05). Post hoc analyses indicated that the effect of OCs on muscle mass increase was induced by the OC-users (n = 7), who used OCs containing 30 μg ethinyl estradiol (EE), whereas the response in users taking OCs with 20 μg EE (n = 7) did not differ from NOC. Both the OC and NOC group experienced an increase in maximal knee strength (p < 0.001) and 1RM leg extension (p < 0.001) after the training period with no difference between groups.

Conclusion: Use of OCs during a 10-week supervised progressive resistance training program was associated with a trend toward a greater increase in muscle mass and a significantly greater increase in type I muscle fiber area compared to controls. Yet, use of OCs did not influence the overall increase in muscle strength related to training.

Brain volumetric alterations accompanied with loss of striatal medium-sized spiny neurons and cortical parvalbumin expressing interneurons in Brd1+/- mice

Schizophrenia is a common and severe mental disorder arising from complex gene-environment interactions affecting brain development and functioning. While a consensus on the neuroanatomical correlates of schizophrenia is emerging, much of its fundamental pathobiology remains unknown. In this study, we explore brain morphometry in mice with genetic susceptibility and phenotypic relevance to schizophrenia (Brd1^+/− mice) using postmortem 3D MR imaging coupled with histology, immunostaining and regional mRNA marker analysis. In agreement with recent large-scale schizophrenia neuroimaging studies, Brd1^+/− mice displayed subcortical abnormalities, including volumetric reductions of amygdala and striatum. Interestingly, we demonstrate that structural alteration in striatum correlates with a general loss of striatal neurons, differentially impacting subpopulations of medium-sized spiny neurons and thus potentially striatal output. Akin to parvalbumin interneuron dysfunction in patients, a decline in parvalbumin expression was noted in the developing cortex of Brd1^+/− mice, mainly driven by neuronal loss within or near cortical layer V, which is rich in corticostriatal projection neurons. Collectively, our study highlights the translational value of the Brd1^+/− mouse as a pre-clinical tool for schizophrenia research and provides novel insight into its developmental, structural, and cellular pathology.

Hyperpolarized [1-13 C]pyruvate MRI can image the metabolic shift in cardiac metabolism between the fasted and fed state in a porcine model

PURPOSE

Owing to its noninvasive nature, hyperpolarized MRI may improve delineation of myocardial metabolic derangement in heart disease. However, consistency may depend on the changeable nature of cardiac metabolism in relation to whole-body metabolic state. This study investigates the impact of feeding status on cardiac hyperpolarized MRI in a large animal model resembling human physiology.

METHODS

Thirteen 30-kg pigs were subjected to an overnight fast, and 5 pigs were fed a carbohydrate-rich meal on the morning of the experiments. Vital parameters and blood samples were registered. All pigs were then scanned by hyperpolarized [1-¹³ C]pyruvate cardiac MRI, and results were compared between the 2 groups and correlated with circulating substrates and hormones.

RESULTS

The fed group had higher blood glucose concentration and mean arterial pressure than the fasted group. Plasma concentrations of free fatty acids (FFAs) were decreased in the fed group, whereas plasma insulin concentrations were similar between groups. Hyperpolarized MRI showed that fed animals had increased lactate/pyruvate, alanine/pyruvate, and bicarbonate/pyruvate ratios. Metabolic ratios correlated negatively with FFA levels.

CONCLUSION

Hyperpolarized MR can identify the effects of different metabolic states on cardiac metabolism in a large animal model. Unlike previous rodent studies, all metabolic derivatives of pyruvate increased in the myocardium of fed pigs. Carbohydrate-rich feeding seems to be a feasible model for standardized, large animal hyperpolarized MRI studies of myocardial carbohydrate metabolism.

No effect of resveratrol on VLDL-TG kinetics and insulin sensitivity in obese men with nonalcoholic fatty liver disease

The present study (NCT01446276, ClinicalTrials.gov) assessed long-term effects of high-dose Resveratrol (RSV) on basal and insulin-mediated very low-density lipoprotein triglyceride (VLDL-TG), palmitate and glucose kinetics, and liver fat content in men with nonalcoholic fatty liver disease (NAFLD). Participants (n = 16) were non-diabetic, upper-body obese (BMI > 28 kg/m² , WHR > 0.9) men with NAFLD who were randomized (1:1) in a double-blinded, placebo-controlled clinical trial to either RSV or placebo (500 mg 3 times daily) for 6 months. Magnetic resonance (MR) spectroscopy, dual-X-ray absorptiometry and MR imaging assessed liver fat content and body composition, respectively. ¹⁴ C-labeled VLDL-TG and ³ H-labeled glucose and palmitate tracers, in combination with indirect calorimetry and breath samples, were used to assess kinetics and substrate oxidations during basal and hyperinsulinaemic euglycaemic clamp conditions. RSV did not improve either basal or insulin-mediated VLDL-TG secretion, oxidation or clearance rates, nor did it affect palmitate or glucose turnover. Likewise, no changes in body composition or liver fat content occurred following RSV compared with placebo treatment. Therefore, RSV cannot be recommended for treatment of metabolic abnormalities in NAFLD.

Evaluation of Active Brown Adipose Tissue by the Use of Hyperpolarized [1-13C]Pyruvate MRI in Mice

The capacity to increase energy expenditure makes brown adipose tissue (BAT) a putative target for treatment of metabolic diseases such as obesity. Presently, investigation of BAT in vivo is mainly performed by fluoro-d-glucose positron emission tomography (FDG PET)/CT. However, non-radioactive methods that add information on, for example, substrate metabolism are warranted. Thus, the aim of this study was to evaluate the potential of hyperpolarized [1-¹³C]pyruvate Magnetic Resonance Imaging (HP-MRI) to determine BAT activity in mice following chronic cold exposure. Cold (6 °C) and thermo-neutral (30 °C) acclimated mice were scanned with HP-MRI for assessment of the interscapular BAT (iBAT) activity. Comparable mice were scanned with the conventional method FDG PET/MRI. Finally, iBAT was evaluated for gene expression and protein levels of the specific thermogenic marker, uncoupling protein 1 (UCP1). Cold exposure increased the thermogenic capacity 3–4 fold (p < 0.05) as measured by UCP1 gene and protein analysis. Furthermore, cold exposure as compared with thermo-neutrality increased iBAT pyruvate metabolism by 5.5-fold determined by HP-MRI which is in good agreement with the 5-fold increment in FDG uptake (p < 0.05) measured by FDG PET/MRI. iBAT activity is detectable in mice using HP-MRI in which potential changes in intracellular metabolism may add useful information to the conventional FDG PET studies. HP-MRI may also be a promising radiation-free tool for repetitive BAT studies in humans.

A randomized placebo-controlled clinical trial of nicotinamide riboside in obese men: safety, insulin-sensitivity, and lipid-mobilizing effects

Background

Animal studies suggest a positive role for nicotinamide riboside (NR) on insulin sensitivity and hepatic steatosis in models of obesity and type 2 diabetes. NR, an NAD+ precursor, is a member of the vitamin B-3 family now available as an over-the-counter supplement. Although data from preclinical trials appear consistent, potential effects and safety need to be evaluated in human clinical trials.

Objective

The aim of this study was to test the safety of dietary NR supplementation over a 12-wk period and potential to improve insulin sensitivity and other metabolic parameters in obese, insulin-resistant men.

Design

In an investigator-initiated randomized, placebo-controlled, double-blinded, and parallel-group designed clinical trial, forty healthy, sedentary men with a body mass index (BMI) > 30 kg/m2, age-range 40-70 y were randomly assigned to 12 wk of NR (1000 mg twice daily) or placebo. We determined the effects of NR supplementation on insulin sensitivity by a hyperinsulinemic euglycemic clamp and substrate metabolism by indirect calorimetry and labeled substrates of tritiated glucose and palmitate. Body composition and fat mass distribution were determined by whole-body dual-energy X-ray absorptiometry (DXA) and MRI scans, and measurements of intrahepatic lipid content were obtained by MR spectroscopy.

Results

Insulin sensitivity, endogenous glucose production, and glucose disposal and oxidation were not improved by NR supplementation. Similarly, NR supplementation had no effect on resting energy expenditure, lipolysis, oxidation of lipids, or body composition. No serious adverse events due to NR supplementation were observed and safety blood tests were normal.

Conclusion

12 wk of NR supplementation in doses of 2000 mg/d appears safe, but does not improve insulin sensitivity and whole-body glucose metabolism in obese, insulin-resistant men. This trial was registered at clinicaltrials.gov as NCT02303483.

Analysis of Velocity in the Ascending Aorta in Humans

To analyze velocity spectral energy distribution in humans, blood velocities were recorded by means of hot-film anemometry at 41 predetermined measurement points in the cross-sectional area of the ascending aorta approximately 6 cm downstream of the aortic valves. Measurements were made in 8 patients with normal aortic valves, in 4 after insertion of a St. Jude Medical (SJM) aortic valve and in 3 after insertion of a Starr-Edwards Silastic Ball (SSB) aortic valve. Data analysis based on Fast Fourier Transform demonstrated that turbulence energy was lower in patients with normal aortic valves than in patients after insertion of an artificial valve in the aortic position and probably more pronounced after SSB valves than after SJM valves. The spatial distribution of the turbulence energy above 100 Hz was more irregular than corresponding laminar velocities previously presented. The Ver100 (Velocity Energy Ratio at 100 Hz, i.e. the velocity energy above 100 Hz divided by the total velocity energy) proved useful for evaluating differences in flow disturbances downstream of different aortic valves. The mean VER100 in the three categories of patients were respectively 0.3, 1.4, and 2.1%.

Three-Dimensional Visualization of Velocity Profiles in the Ascending Aorta in Humans

Blood velocities were recorded intraoperatively in the ascending aorta approximately 6 cm downstream of the aortic annulus in eight patients with normal aortic valves (prior to coronary bypass surgery) and in seven patients after implantation of a St. Jude Medical valve (4) or Starr-Edwards Silastic Ball valve (3) in the aortic position by means of constant temperature hot-film anemometry. The velocities were measured during 5-15 heart cycles at 41 predetermined measurement points almost evenly distributed in the cross sectional area. Velocity profiles were visualized three-dimensionally at 100 time intervals during one mean heart cycle. The standard deviation of velocities was correspondingly three-dimensionally visualized. For the patients with normal aortic valves the velocity profiles were generally flat but skew, with the highest velocity closer to the left vessel wall at the start of systole. During systole the skewness turned counterclockwise with the highest velocities closer to the posterior, right and finally anterior vessel wall at the end of systole. In patients with an artificial heart valve in the aortic position the design of the valve was reflected on the contour of the profiles. The findings correspond well with model studies.

Escitalopram Ameliorates Hypercortisolemia and Insulin Resistance in Low Birth Weight Men With Limbic Brain Alterations

CONTEXT

Low birth weight (LBW; <2500 g) is linked to the development of insulin resistance and limbic-hypothalamic-pituitary-adrenal (LHPA) axis hyperactivity.

OBJECTIVE

Our first aim was to study insulin action, LHPA axis function, and limbic brain structures in young, healthy LBW men vs normal birthweight (NBW) controls (part 1). Our second aim was to investigate the effects of escitalopram vs placebo in LBW men in the LHPA axis and insulin sensitivity (part 2).

DESIGN SETTING, PARTICIPANTS, AND INTERVENTION

The maximal (Rdmax) and submaximal (Rdsubmax) rates of insulin-stimulated glucose turnover, LHPA axis, and brain morphology were examined in 40 LBW men and 20 matched NBW men using two-stage hyperinsulinemic euglycemic clamp, 24-hour hormone plasma profiles, and magnetic resonance imaging. Subsequently, all LBW subjects underwent randomized and double-blind treatment with escitalopram 20 mg/d or placebo for 3 months followed by a complete reexamination.

MAIN OUTCOME MEASURES (PART 2)

Changes in Rdmax/Rdsubmax and plasma-free cortisol 24-hour area under the curve.

RESULTS

In LBW vs NBW, Rdsubmax and Rdmax were ∼16% (P = 0.01) and ∼12% (P = 0.01) lower, respectively, and 24-hour free cortisol levels were ∼20% higher (P = 0.02), primarily driven by a ∼99% increase at 05:00 am (P < 0.001). Furthermore, these changes were related to structural alterations within left thalamus and ventromedial prefrontal cortex. However, in LBW men, exposure to escitalopram normalized the free cortisol levels and improved the Rdsubmax by ∼24% (P = 0.04) compared with placebo.

CONCLUSIONS

LBW vs NBW displayed alterations in key brain structures modulating the LHPA axis, elevated free cortisol levels, and insulin resistance. Escitalopram administration ameliorated these defects, suggesting a potential for LHPA axis modulation compounds to improve insulin action in LBW subjects.

Hyperpolarized [1-13C]-acetate Renal Metabolic Clearance Rate Mapping

¹¹C-acetate is a positron emission tomography (PET) tracer of oxidative metabolism, whereas hyperpolarized ¹³C-acetate can be used in magnetic resonance imaging (MRI) for investigating specific metabolic processes. The aims of this study were to examine if the kinetic formalism of ¹¹C-acetate PET in the kidneys is comparable to that of ¹³C-acetate MRI, and to compare the dynamic metabolic information of hyperpolarized ¹³C-acetate MRI with that obtained with ¹¹C-acetate PET. Rats were examined with dynamic hyperpolarized ¹³C-acetate MRI or ¹¹C-acetate PET before and after intravenous injection of furosemide, a loop diuretic known to alter both the hemodynamics and oxygen consumption in the kidney. The metabolic clearance rates (MCR) were estimated and compared between the two modalities experimentally in vivo and in simulations. There was a clear dependency on the mean transit time and MCR for both ¹³C-acetate and ¹¹C-acetate following furosemide administration, while no dependencies on the apparent renal perfusion were observed. This study demonstrated that hyperpolarized ¹³C-acetate MRI is feasible for measurements of the intrarenal energetic demand via the MCR, and that the quantitative measures are correlated with those measured by ¹¹C-acetate PET, even though the temporal window is more than 30 times longer with ¹¹C-acetate.

The potential of hyperpolarized 13C magnetic resonance spectroscopy to monitor the effect of combretastatin based vascular disrupting agents

BACKGROUND

Targeting tumor vasculature with vascular disrupting agents (VDAs) results in substantial cell death that precede tumor shrinkage. Here, we investigate the potential of hyperpolarized magnetic resonance spectroscopy (HPMRS) to monitor early metabolic changes associated with VDA treatment.

METHODS

Mice bearing C3H mammary carcinomas were treated with the VDAs combretastatin-A4-phosphate (CA4P) or the analog OXi4503, and HPMRS was performed following [1-¹³C]pyruvate administration. Similarly, treated mice were positron emission tomography (PET) scanned following administration of the glucose analog FDG. Finally, metabolic imaging parameters were compared to tumor regrowth delay and measures of vascular damage, derived from dynamic contrast-agent enhanced magnetic resonance imaging (DCE-MRI) and histology.

RESULTS

VDA-treatment impaired tumor perfusion (histology and DCE-MRI), reduced FDG uptake, increased necrosis, and slowed tumor growth. HPMRS, revealed that the [1-¹³C]pyruvate-to-[1-¹³C]lactate conversion remained unaltered, whereas [1-¹³C]lactate-to-[¹³C]bicarbonate (originating from respiratory CO₂) ratios increased significantly following treatment.

CONCLUSIONS

DCE-MRI and FDG-PET revealed loss of vessel functionality, impaired glucose delivery and reduced metabolic activity prior to cell death. [1-¹³C]lactate-to-[¹³C]bicarbonate ratios increased significantly during treatment, indicating a decline in respiratory activity driven by the onset of hypoxia. HPMRS is promising for early detection of metabolic stress inflicted by VDAs, which cannot easily be inferred based on blood flow measurements.

Hyperpolarized 13C Magnetic Resonance Imaging Can Detect Metabolic Changes Characteristic of Penumbra in Ischemic Stroke

Magnetic resonance imaging (MRI) is increasingly the method of choice for rapid stroke assessment in patients and for guiding patient selection in clinical trials. The underlying metabolic status during stroke and following treatment is recognized as an important prognostic factor; thus, new methods are required to monitor local biochemistry following cerebral infarction, rapidly and in vivo. Hyperpolarized MRI with the tracer [1-¹³C]pyruvate enables rapid detection of localized [1-¹³C]lactate production, which has recently been shown in patients, supporting its translation to assess clinical stroke. Here we show the ability of hyperpolarized ¹³C MRI to detect the metabolic alterations characteristic of endothelin-1-induced ischemic stroke in rodents. In the region of penumbra, determined via T2-weighted ¹H MRI, both [1-¹³C]pyruvate delivery and [1-¹³C]pyruvate cellular uptake independently increased. Furthermore, we observed a 33% increase in absolute [1-¹³C]lactate signal in the penumbra, and we determined that half of this increase was due to increased intracellular [1-¹³C]pyruvate supply and half was mediated by enhanced lactate dehydrogenase-mediated [1-¹³C]lactate production. Future work to characterize the kinetics of delivery, uptake, and enzymatic conversions of hyperpolarized tracers following ischemic stroke could position hyperpolarized ¹³C MRI as an ideal technology for rapid assessment of the penumbra during the critical time window following ischemic stroke in patients.

No Beneficial Effects of Resveratrol on the Metabolic Syndrome: A Randomized Placebo-Controlled Clinical Trial

CONTEXT

Low-grade inflammation is associated with obesity and the metabolic syndrome (MetS). Preclinical evidence suggests that resveratrol (RSV) has beneficial metabolic and anti-inflammatory effects that could have therapeutic implications.

OBJECTIVE

To investigate effects of long-term RSV treatment on inflammation and MetS.

SETTING AND DESIGN

A randomized, placebo-controlled, double-blind, parallel group clinical trial conducted at Aarhus University Hospital.

PARTICIPANTS

Middle-aged community-dwelling men (N = 74) with MetS, 66 of whom completed all visits (mean ± standard error of the mean): age, 49.5 ± 0.796 years; body mass index, 33.8 ± 0.44 kg/m2; waist circumference, 115 ± 1.14 cm.

INTERVENTION

Daily oral supplementation with 1000 mg RSV (RSVhigh), 150 mg RSV, or placebo for 16 weeks.

MAIN OUTCOME MEASURES

Plasma levels of high-sensitivity C-reactive protein (hs-CRP), circulating lipids, and inflammatory markers in circulation and adipose/muscle tissue biopsy specimens; glucose metabolism; and body composition including visceral fat and ectopic fat deposition.

RESULTS

RSV treatment did not lower circulating levels of hs-CRP, interleukin 6, or soluble urokinase plasminogen activator receptor in plasma, and inflammatory gene expression in adipose and muscle tissues also remained unchanged. RSV treatment had no effect on blood pressure, body composition, and lipid deposition in the liver or striated muscle. RSV treatment had no beneficial effect on glucose or lipid metabolism. RSVhigh treatment significantly increased total cholesterol (P < 0.002), low-density lipoprotein (LDL) cholesterol (P < 0.006), and fructosamine (P < 0.013) levels compared with placebo.

CONCLUSION

RSV treatment did not improve inflammatory status, glucose homeostasis, blood pressure, or hepatic lipid content in middle-aged men with MetS. On the contrary, RSVhigh significantly increased total cholesterol, LDL cholesterol, and fructosamine levels compared with placebo.

Substrate Metabolism and Insulin Sensitivity During Fasting in Obese Human Subjects: Impact of GH Blockade

CONTEXT

Insulin resistance and metabolic inflexibility are features of obesity and are amplified by fasting. Growth hormone (GH) secretion increases during fasting and GH causes insulin resistance.

OBJECTIVE

To study the metabolic effects of GH blockade during fasting in obese subjects.

SUBJECTS AND METHODS

Nine obese males were studied thrice in a randomized design: (1) after an overnight fast (control), (2) after 72 hour fasting (fasting), and (3) after 72 hour fasting with GH blockade (pegvisomant) [fasting plus GH antagonist (GHA)]. Each study day consisted of a 4-hour basal period followed by a 2-hour hyperinsulinemic, euglycemic clamp combined with indirect calorimetry, assessment of glucose and palmitate turnover, and muscle and fat biopsies.

RESULTS

GH levels increased with fasting (P < 0.01), and the fasting-induced reduction of serum insulin-like growth factor I was enhanced by GHA (P < 0.05). Fasting increased lipolysis and lipid oxidation independent of GHA, but fasting plus GHA caused a more pronounced suppression of lipid intermediates in response to hyperinsulinemic, euglycemic clamp. Fasting-induced insulin resistance was abrogated by GHA (P < 0.01) primarily due to reduced endogenous glucose production (P = 0.003). Fasting plus GHA also caused elevated glycerol levels and reduced levels of counterregulatory hormones. Fasting significantly reduced the expression of antilipolytic signals in adipose tissue independent of GHA.

CONCLUSIONS

Suppression of GH activity during fasting in obese subjects reverses insulin resistance and amplifies insulin-stimulated suppression of lipid intermediates, indicating that GH is an important regulator of substrate metabolism, insulin sensitivity, and metabolic flexibility also in obese subjects.

In situ lactate dehydrogenase activity: a novel renal cortical imaging biomarker of tubular injury?

Renal ischemia-reperfusion injury is the state of which a tissue experiences injury after a phase of restrictive blood supply and recirculation. Ischemia-reperfusion injury (I/R-I) is a leading cause of acute kidney injury (AKI) in several disease states, including kidney transplantation, sepsis, and hypovolemic shock. The most common methods to evaluate AKI are creatinine clearance, plasma creatinine, blood urea nitrogen, or renal histology. However, currently, there are no precise methods to directly assess renal injury state noninvasively. Hyperpolarized 13C-pyruvate MRI enables noninvasive accurate quantification of the in vivo conversion of pyruvate to lactate, alanine, and bicarbonate. In the present study, we investigated the in situ alterations of metabolic conversion of pyruvate to lactate, alanine, and bicarbonate in a unilateral I/R-I rat model with 30 min and 60 min of ischemia followed by 24 h of reperfusion. The pyruvate conversion was unaltered compared with sham in the 30 min I/R-I group, while a significant reduced metabolic conversion was found in the postischemic kidney after 60 min of ischemia. This indicates that after 30 min of ischemia, the kidney maintains normal metabolic function in spite of decreased kidney function, whereas the postischemic kidney after 60 min of ischemia show a generally reduced metabolic enzyme activity concomitant with a reduced kidney function. We have confidence that these findings can have a high prognostic value in prediction of kidney injury and the outcome of renal injury.

Antioxidant treatment attenuates lactate production in diabetic nephropathy

The early progression of diabetic nephropathy is notoriously difficult to detect and quantify before the occurrence of substantial histological damage. Recently, hyperpolarized [1-13C]pyruvate has demonstrated increased lactate production in the kidney early after the onset of diabetes, implying increased lactate dehydrogenase activity as a consequence of increased nicotinamide adenine dinucleotide substrate availability due to upregulation of the polyol pathway, i.e., pseudohypoxia. In this study, we investigated the role of oxidative stress in mediating these metabolic alterations using state-of-the-art hyperpolarized magnetic resonance (MR) imaging. Ten-week-old female Wistar rats were randomly divided into three groups: healthy controls, untreated diabetic (streptozotocin treatment to induce insulinopenic diabetes), and diabetic, receiving chronic antioxidant treatment with TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) via the drinking water. Examinations were performed 2, 3, and 4 wk after the induction of diabetes by using a 3T Clinical MR system equipped with a dual tuned 13C/1H-volume rat coil. The rats received intravenous hyperpolarized [1-13C]pyruvate and were imaged using a slice-selective 13C-IDEAL spiral sequence. Untreated diabetic rats showed increased renal lactate production compared with that shown by the controls. However, chronic TEMPOL treatment significantly attenuated diabetes-induced lactate production. No significant effects of diabetes or TEMPOL were observed on [13C]alanine levels, indicating an intact glucose-alanine cycle, or [13C]bicarbonate, indicating normal flux through the Krebs cycle. In conclusion, this study demonstrates that diabetes-induced pseudohypoxia, as indicated by an increased lactate-to-pyruvate ratio, is significantly attenuated by antioxidant treatment. This demonstrates a pivotal role of oxidative stress in renal metabolic alterations occurring in early diabetes.

Placebo-controlled, randomised clinical trial: high-dose resveratrol treatment for non-alcoholic fatty liver disease

OBJECTIVE

"The obesity epidemic" has led to an increase in obesity-related conditions including non-alcoholic fatty liver disease (NAFLD), for which effective treatments are in demand. The polyphenol resveratrol prevents the development of experimental NAFLD through modulation of cellular pathways involved in calorie restriction. We aimed to test the hypothesis that resveratrol alleviates NAFLD in a randomised, clinical trial.

MATERIALS AND METHODS

A total of 28 overweight patients with transaminasemia and histological NAFLD were randomised 1:1 to placebo or resveratrol 1.5 g daily for 6 months. Twenty-six participants completed the trial and underwent repeated clinical investigation, blood work, MR spectroscopy; and 19 participants agreed to a repeat liver biopsy.

RESULTS

Resveratrol treatment was generally not superior to placebo in improving plasma markers of liver injury (primary outcome: alanine transaminase, p = 0.51). Resveratrol-treated patients showed a 3.8% decrease in liver lipid content (p = 0.03), with no difference between the two treatment arms (p = 0.38) and no improvement of histological features. Resveratrol treatment was not associated with improvements in insulin sensitivity or markers of the metabolic syndrome, except for a transient decrease in systolic BP. Microarray analysis and qRT-PCR revealed no major changes in expression profile. Also, we report a serious adverse event in a patient who developed fever and bicytopenia.

CONCLUSIONS

In this placebo-controlled, high-dose and long-term study, resveratrol treatment had no consistent therapeutic effect in alleviating clinical or histological NAFLD, though there may be a small ameliorating effect on liver function tests and liver fat accumulation.

Systematized water content calculation in cartilage using T1-mapping MR estimations: design and validation of a mathematical model

Background

Up to 80 % of cartilage is water; the rest is collagen fibers and proteoglycans. Magnetic resonance (MR) T1-weighted measurements can be employed to calculate the water content of a tissue using T1 mapping. In this study, a method that translates T1 values into water content data was tested statistically.

Materials and methods

To develop a predictive equation, T1 values were obtained for tissue-mimicking gelatin samples. 1.5 T MRI was performed using inverse angle phase and an inverse sequence at 37 (±0.5) °C. Regions of interest were manually delineated and the mean T1 value was estimated in arbitrary units. Data were collected and modeled using linear regression. To validate the method, articular cartilage from six healthy pigs was used. The experiment was conducted in accordance with the Danish Animal Experiment Committee. Double measurements were performed for each animal. Ex vivo, all water in the tissue was extracted by lyophilization, thus allowing the volume of water to be measured. This was then compared with the predicted water content via Lin’s concordance correlation coefficient at the 95 % confidence level.

Results

The mathematical model was highly significant when compared to a null model (p < 0.0001). 97.3 % of the variation in water content can be explained by absolute T1 values. Percentage water content could be predicted as 0.476 + (T1 value) × 0.000193 × 100 %. We found that there was 98 % concordance between the actual and predicted water contents.

Conclusion

The results of this study demonstrate that MR data can be used to predict percentage water contents of cartilage samples.

Level of evidence

3 (case-control study).

Hyperpolarized 13 C,15 N2 -Urea MRI for assessment of the urea gradient in the porcine kidney

PURPOSE

A decline in cortico-medullary osmolality gradient of the kidney may serve as an early indicator of pathological disruption of the tubular reabsorption process. The purpose of this study was to investigate the feasibility of hyperpolarized ¹³ C,¹⁵ N₂ -urea MRI as a biomarker of renal function in healthy porcine kidneys resembling the human physiology.

METHODS

Five healthy female Danish domestic pigs (weight 30 kg) were scanned at 3 Tesla (T) using a ¹³ C 3D balanced steady-state MR pulse sequence following injection of hyperpolarized ¹³ C,¹⁵ N₂ -urea via a femoral vein catheter. Images were acquired at different time points after urea injection, and following treatment with furosemide.

RESULTS

A gradient in cortico-medullary urea was observed with an intramedullary accumulation 75 s after injection of hyperpolarized ¹³ C,¹⁵ N₂ -urea, whereas images acquired at earlier time points postinjection were dominated by cortical perfusion. Furosemide treatment resulted in an increased urea accumulation in the cortical space, leading to a reduction of the medullary-to-cortical signal ratio of 49%.

CONCLUSION

This study demonstrates that hyperpolarized ¹³ C,¹⁵ N₂ -urea MRI is capable of identifying the intrarenal accumulation of urea and can differentiate acute renal functional states in multipapillary kidneys, highlighting the potential for human translation. Magn Reson Med 76:1895-1899, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Does radiofrequency ablation (RFA) epiphysiodesis affect adjacent joint cartilage?

PURPOSE

To test the hypothesis that epiphysiodesis made with radiofrequency ablation (RFA) is a safe procedure that disrupts the growth plate without damaging the adjacent joint articular cartilage.

METHODS

RFA epiphysiodesis was done during 8 min in vivo in 40 growing pig tibia physis. In addition, three tibiae were ablated for 16 min and three more for 24 min. As a burned cartilage reference, six tibiae were ablated on the joint articular cartilage for 8 min. After the procedure, the animals were terminated and the tibiae were harvested. Magnetic resonance imaging (MRI) was done ex vivo to evaluate the joint articular cartilage in all samples. We used T1-weighted, T2-weighted, and water content sequences under a 1.5 T magnetic field.

RESULTS

On the burned articular cartilage, intensity changes were observed at MRI. We found no evidence of articular cartilage damage on the 40 8-min RFA procedures. The tibiae ablated for 16 min and 24 min showed intact joint cartilage.

CONCLUSIONS

Epiphysiodesis using RFA is safe for the adjacent articular cartilage. This study shows that RFA can be done safely in the growing physis of pigs, even with triple duration procedures.

The frequently used intraperitoneal hyponatraemia model induces hypovolaemic hyponatraemia with possible model-dependent brain sodium loss

NEW FINDINGS

What is the central question of this study? The brain response to acute hyponatraemia is usually studied in rodents by intraperitoneal instillation of hypotonic fluids (i.p. model). The i.p. model is described as 'dilutional' and 'syndrome of inappropriate ADH (SIADH)', but the mechanism has not been explored systematically and might affect the brain response. Therefore, in vivo brain and muscle response were studied in pigs. What is the main finding and its importance? The i.p. model induces hypovolaemic hyponatraemia attributable to sodium redistribution, not dilution. A large reduction in brain sodium is observed, probably because of the specific mechanism causing the hyponatraemia. This is not accounted for in current understanding of the brain response to acute hyponatraemia. Hyponatraemia is common clinically, and if it develops rapidly, brain oedema evolves, and severe morbidity and even death may occur. Experimentally, acute hyponatraemia is most frequently studied in small animal models, in which the hyponatraemia is produced by intraperitoneal instillation of hypotonic fluids (i.p. model). This hyponatraemia model is described as 'dilutional' or 'syndrome of inappropriate ADH (SIADH)', but seminal studies contradict this interpretation. To confront this issue, we developed an i.p. model in a large animal (the pig) and studied water and electrolyte responses in brain, muscle, plasma and urine. We hypothesized that hyponatraemia was induced by simple water dilution, with no change in organ sodium content. Moderate hypotonic hyponatraemia was induced by a single i.v. dose of desmopressin and intraperitoneal instillation of 2.5% glucose. All animals were anaesthetized and intensively monitored. In vivo brain and muscle water was determined by magnetic resonance imaging and related to the plasma sodium concentration. Muscle water content increased less than expected as a result of pure dilution, and muscle sodium content decreased significantly (by 28%). Sodium was redistributed to the peritoneal fluid, resulting in a significantly reduced plasma volume. This shows that the i.p. model induces hypovolaemic hyponatraemia and not dilutional/SIADH hyponatraemia. Brain oedema evolved, but brain sodium content decreased significantly (by 21%). To conclude, the i.p. model induces hypovolaemic hyponatraemia attributable to sodium redistribution and not water dilution. The large reduction in brain sodium is probably attributable to the specific mechanism that causes the hyponatraemia. This is not accounted for in the current understanding of the brain response to acute hyponatraemia.

Diabetes induced renal urea transport alterations assessed with 3D hyperpolarized 13 C,15 N-Urea

PURPOSE

In the current study, we investigated hyperpolarized urea as a possible imaging biomarker of the renal function by means of the intrarenal osmolality gradient.

METHODS

Hyperpolarized three-dimensional balanced steady state ¹³ C MRI experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements was performed on two groups of rats, a streptozotocin type 1 diabetic group and a healthy control group.

RESULTS

A significant decline in intrarenal steepness of the urea gradient was found after 4 weeks of untreated insulinopenic diabetes in agreement with an increased urea transport transcription.

CONCLUSION

MRI and hyperpolarized [¹³ C,¹⁵ N]urea can monitor the changes in the corticomedullary urea concentration gradients in diabetic and healthy control rats. Magn Reson Med 77:1650-1655, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Impaired Insulin Suppression of VLDL-Triglyceride Kinetics in Nonalcoholic Fatty Liver Disease

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is associated with glucose and lipid metabolic abnormalities. However, insulin suppression of very low-density lipoprotein-triglyceride (VLDL-TG) kinetics is not fully understood.

OBJECTIVE

The objective of the study was to determine VLDL-TG, glucose, and palmitate kinetics during fasting and hyperinsulinemia in men with (NAFLD+) and without NAFLD (NAFLD−).

DESIGN

Twenty-seven nondiabetic, upper-body obese (waist to hip ratio > 0.9, body mass index > 28 kg/m2) men, 18 NAFLD+, and nine NAFLD− determined by magnetic resonance spectroscopy were enrolled.14C-labeled VLDL-TG and 3H-labeled glucose and palmitate tracers were applied in combination with indirect calorimetry and breath samples to assess kinetics and substrate oxidations postabsorptively and during a hyperinsulinemic-euglycemic clamp. Dual-X-ray absorptiometry and magnetic resonance imaging assessed body composition.

RESULTS

Liver fat content was greater in NAFLD+ than NAFLD− men (21.0% vs 3.7%), even though body composition, metabolites (except triglycerides), and insulin were similar in the groups. Insulin suppression of VLDL-TG secretion (P = .0001), oxidation (P = .0003), and concentration (P= .008) as well as percentage decreases were lower in NAFLD+ than NAFLD− men (secretion: 31.9% ± 17.2% vs 64.7% ± 19.9%; oxidation: −9.0% ± 24.7% vs 46.5% ± 36.6%; concentration: 11.9% ± 20.7% vs 56.2% ± 22.9%, all P < .001). Likewise, lower insulin suppression of very low-density lipoprotein particle size was present in NAFLD+ than NAFLD− men (P = .0002). Conversely, insulin suppression of endogenous glucose production was similar in the groups.

CONCLUSIONS

Compared with endogenous glucose production, the inability of NAFLD+ men to suppress VLDL-TG kinetics to compensate for the increased liver fat content seems to be an early pathophysiological manifestation of male NAFLD+. These data suggest therapeutic targets reducing liver fat content may ameliorate metabolic abnormalities associated with NAFLD and presumably diabetes.

Hyperpolarized magnetic resonance spectroscopy for assessing tumor hypoxia

INTRODUCTION

Hypoxic tumor cells are radioresistant, therefore, identification of hypoxia is crucial. Hyperpolarized magnetic resonance spectroscopy (HPMRS) allows real time measurements of the conversion of pyruvate to lactate, the final step of anaerobic energy production, and may thus allow non-invasive identification of hypoxia or treatment-induced changes in oxygenation. The aim of the study was to investigate the usefulness of HPMRS as a means to assess tumor hypoxia and its dynamics during intervention.

MATERIAL AND METHODS

C3H mammary carcinomas grown in CDF1 mice were used. To manipulate with tumor oxygenation, non-anaesthetized mice were gassed with air, 10% or 100% oxygen prior to administration of hyperpolarized [1-¹³C]pyruvate and HPMRS analysis. A direct assessment of tumor oxygen partial pressure (pO2) distributions were made using the Eppendorf oxygen electrode in a separate, but similarly treated, group of mice.

RESULTS

Even though breathing 100% oxygen improved tumor oxygenation as evidenced by pO2 measurements, the mean (with 1 S.E.) [1-¹³C]lactate/[1-¹³C]pyruvate ratio was unaffected by this intervention, being 34 (30-37) in mice breathing air and 37 (33-42) in mice breathing 100% oxygen. In contrast, and in accordance with pO2 measurements, a significant increase in the [1-¹³C]lactate/[1-¹³C]pyruvate ratio was seen in 10% oxygen-breathing mice with a ratio of 46 (42-50).

CONCLUSIONS

Although, no metabolic change was observed during 100% O2 breathing using HPMRS, the significant increase in the [1-¹³C]lactate/[1-¹³C]pyruvate ratio during 10% oxygen breathing suggests, that HPMRS can detect hypoxia-driven changes in the metabolic fate of pyruvate. To what extent and for what purposes HPMRS may best supplement or complement established techniques like hypoxia PET needs to be unraveled in future research.

Investigation of metabolic changes in STZ-induced diabetic rats with hyperpolarized [1-13C]acetate

In the metabolism of acetate several enzymes are involved, which play an important role in free fatty acid oxidation. Fatty acid metabolism is altered in diabetes patients and therefore acetate might serve as a marker for pathological changes in the fuel selection of cells, as these changes occur in diabetes patients. Acetylcarnitine is a metabolic product of acetate, which enables its transport into the mitochondria for energy production. This study investigates whether the ratio of acetylcarnitine to acetate, measured by noninvasive hyperpolarized [1-¹³C]acetate magnetic resonance spectroscopy, could serve as a marker for myocardial, hepatic, and renal metabolic changes in rats with Streptozotocin (STZ)-induced diabetes in vivo. We demonstrate that the conversion of acetate to acetylcarnitine could be detected and quantified in all three organs of interest. More interestingly, we found that the hyperpolarized acetylcarnitine to acetate ratio was independent of blood glucose levels and prolonged hyperglycemia following diabetes induction in a type-1 diabetes model.

Acute porcine renal metabolic effect of endogastric soft drink administration assessed with hyperpolarized [1-(13)C]pyruvate

PURPOSE

Our aim was to determine the quantitative reproducibility of metabolic breakdown products in the kidney following intravenous injection of hyperpolarized [1-(13)C]pyruvate and secondly to investigate the metabolic effect on the pyruvate metabolism of oral sucrose load using dissolution dynamic nuclear polarization. By this technique, metabolic alterations in several different metabolic related diseases and their metabolic treatment responses can be accessed.

METHODS

In four healthy pigs the lactate-to-pyruvate, alanine-to-pyruvate and bicarbonate-to-pyruvate ratio was measured following administration of regular cola and consecutive injections of hyperpolarized [1-(13)C]pyruvate four times within an hour.

RESULTS

The overall lactate-to-pyruvate metabolic profile changed significantly over one hour following an acute sucrose load leading to a significant rise in blood glucose.

CONCLUSION

The reproducibility of hyperpolarized magnetic resonance spectroscopy in the healthy pig kidney demonstrated a repeatability of more than 94% for all metabolites and, furthermore, that the pyruvate to lactate conversion and the blood glucose level is elevated following endogastric sucrose administration.

Adipose tissue, estradiol levels, and bone health in obese men with metabolic syndrome

OBJECTIVE

Visceral adipose tissue (VAT) is associated with an increased risk of metabolic syndrome (MetS). Recent studies have suggested that VAT negatively affects bone. However, MetS has also been associated with higher estradiol (E2) levels, which is bone protective. We therefore investigated the impact of VAT and E2 levels on bone density, structural parameters, and strength estimates.

DESIGN

A cross-sectional study was conducted in 72 obese men with MetS to investigate the impact of VAT and E2 levels on bone.

METHODS

Bone parameters were assessed by dual-energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT), and high-resolution peripheral QCT (HRpQCT) at lumbar spine, proximal femur, radius, and tibia. VAT volume was measured by magnetic resonance imaging (MRI) and sexual hormones were measured in blood samples.

RESULTS

Men with high VAT had a lower bone density at the hip (P<0.05), lower cortical thickness, and higher buckling ratio at femoral neck (FN) (P=0.008 and P=0.02), compared with men with low VAT, despite a similar body weight and BMI. Generally, E2 levels were low (median 43 pmol/l), and men with E2 levels below median had reduced bone density at lumbar spine (P=0.04), and impaired structural parameters at radius and tibia, compared with men with E2 levels above median. At the hip, VAT volume and E2 levels affected bone density independently and additively, and 50% of men with high VAT and low E2 levels had osteopenia with significantly lower T-score at FN (P=0.004).

CONCLUSIONS

High VAT and low E2 negatively affect bone in obese men with MetS. VAT and E2 affect bone density at the hip independently and additively, revealing an unexpected high prevalence of osteopenia in middle-aged men with MetS.

Reduced CD300LG mRNA tissue expression, increased intramyocellular lipid content and impaired glucose metabolism in healthy male carriers of Arg82Cys in CD300LG: a novel genometabolic cross-link between CD300LG and common metabolic phenotypes

BACKGROUND

CD300LG rs72836561 (c.313C>T, p.Arg82Cys) has in genetic-epidemiological studies been associated with the lipoprotein abnormalities of the metabolic syndrome. CD300LG belongs to the CD300-family of membrane-bound molecules which have the ability to recognize and interact with extracellular lipids. We tested whether this specific polymorphism results in abnormal lipid accumulation in skeletal muscle and liver and other indices of metabolic dysfunction.

METHODS

40 healthy men with a mean age of 55 years were characterized metabolically including assessment of insulin sensitivity by the hyperinsulinemic euglycemic clamp, intrahepatic lipid content (IHLC) and intramyocellular lipid content (IMCL) by MR spectroscopy, and β-cell function by an intravenous glucose tolerance test. Changes in insulin signaling and CD300LG mRNA expression were determined by western blotting and quantitative PCR in muscle and adipose tissue.

RESULTS

Compared with the 20 controls (CC carriers), the 20 CT carriers (polymorphism carriers) had higher IMCL (p=0.045), a reduced fasting forearm glucose uptake (p=0.011), a trend toward lower M-values during the clamp; 6.0 mg/kg/min vs 7.1 (p=0.10), and higher IHLC (p=0.10). CT carriers had lower CD300LG mRNA expression and CD300LG expression in muscle correlated with IMCL (β=-0.35, p=0.046), forearm glucose uptake (β=0.37, p=0.03), and tended to correlate with the M-value (β=0.33, p=0.06), independently of CD300LG genotype. β-cell function was unaffected.

CONCLUSIONS

The CD300LG polymorphism was associated with decreased CD300LG mRNA expression in muscle and adipose tissue, increased IMCL, and abnormalities of glucose metabolism. CD300LG mRNA levels correlated with IMCL and forearm glucose uptake. These findings link a specific CD300LG polymorphism with features of the metabolic syndrome suggesting a role for CD300LG in the regulation of common metabolic traits.

TRIAL REGISTRATION NUMBER

NCT01571609.

Intrahepatic fat content correlates with soluble CD163 in relation to weight loss induced by Roux-en-Y gastric bypass

OBJECTIVE

Soluble CD163 (sCD163) is a new marker of obesity-related metabolic complications. sCD163 and CD163 mRNA were investigated in relation to the fat distribution at baseline and 12 months after Roux-en-Y gastric bypass (RYGB).

METHODS

Thirty-one obese subjects (BMI: 42.3 ± 4.7 kg/m(2)) were enrolled. Subcutaneous (SAT) and visceral adipose tissue (VAT) volume were determined by MRI, intrahepatic lipid content (IHL) by MR-spectroscopy, and body composition by DXA. Fasting blood samples and adipose tissue samples were obtained, and ELISA and RT-PCR were performed.

RESULTS

RYGB-induced weight loss (36 ± 11 kg) was accompanied by a significant reduction in sCD163 (2.1 ± 0.8 mg/l vs. 1.7 ± 0.7 mg/l), SAT, VAT, and IHL (all, P < 0.001). At baseline, sCD163 was associated with VAT (r = 0.40, P < 0.05) but not with SAT or IHL. Moreover, CD163 mRNA was significantly upregulated in VAT compared with SAT at baseline (P < 0.05) and significantly downregulated in SAT after RYGB (P < 0.001). ΔsCD163 was significantly associated with ΔIHL after RYGB compared with baseline (r = 0.40, P < 0.05).

CONCLUSIONS

RYGB-induced weight loss results in a reduction of sCD163 and CD163 mRNA. The association between ΔsCD163 and ΔIHL may reflect a reduction in sCD163-producing Kupffer cells in the liver. Moreover, sCD163 may be a marker of "unhealthy" fat distribution in obese subjects.

Thermal epiphysiodesis performed with radio frequency in a porcine model

BACKGROUND AND PURPOSE

Current techniques for epiphysiodesis involve opening of cortical windows; use of staples, screws, and tension devices; and fusion with curettes or drills. Complications may have serious consequences. There is a need for a more reliable, precise, and less traumatic procedure that overcomes the known complications from existing techniques. We analyzed a new epiphysiodesis technique using radio-frequency ablation (RFA) in a porcine model.

METHODS

Six 35-kg and two 25-kg immature pigs were used. 1 hind leg of each animal was randomly selected and the proximal tibia growth plate was ablated laterally and medially. The contralateral leg was used as a control. MR images were obtained immediately after the ablation and 12 weeks later for 6 animals, and 24 weeks later for the other 2 animals. CT was done for the 2 animals that were followed for 24 weeks for proof of bone bridges.

RESULTS

Both tibias were equal in length initially. At the 12-week follow-up, there was an average leg length discrepancy of 3.9 mm (95% CI: 3.0-4.8), and at 24 weeks the difference was 8.4 mm and 7.5 mm. No damage to the adjacent tissue was found. Bone bridges and physeal closure were found after 24 weeks. The pigs showed no discomfort after the intervention.

INTERPRETATION

We found RFA to be feasible for epiphysiodesis in a pig model. The method is minimally invasive and recovery may be quick compared to conventional methods. We recommend that the method should be tested in larger-scale safety studies before clinical application.

Accuracy of MR in growth plate measurement

PURPOSE

To analyze the accuracy of growth-plate thickness measurements detected on 1.5-T and 7-T MR images using histology sections as a standard of reference.

MATERIALS AND METHODS

Four defrosted pig tibiae were 1.5-T MR scanned and one fresh tibia was 7-T MR scanned. The height of the growth plate was measured and compared to histology.

RESULTS

Histology measurements showed a mean growth plate thickness of 467 μm (SD = 82.2). The mean growth plate thickness measured in the 7-T MR images was 465 μm (SD = 62.2) and 1,325 μm (SD = 183.5) on 1.5-T MR measurements. We found a better correspondence between the growth plate thickness measured on the 7-T MR and histology samples compared to 1.5 T.

CONCLUSIONS

The growth plate can be identified and measured with high accuracy using 7-T MR. 1.5-T MR can only describe some morphological characteristics.

[Quantitative cellular metabolism can be estimated by hyperpolarized magnetic resonance]

A new MR methodology, hyperpolarized MR spectroscopy (MRS), enhances the MRS signals by more than a factor 10,000, enabling fast and unique insight into in situ metabolic processes. So far the method has provided new and exciting metabolic details in prostate, heart, brain, kidney and liver examinations. In diseases characterized by abnormal metabolic profiles, such as in diabetes and tumour tissue, hyperpolarized MRS provides highly detailed spatial information as well as quantitative estimates of individual steps in glycolysis and real-time amino acid metabolism.

Concomitant changes in cross-sectional area and water content in skeletal muscle after resistance exercise

This study investigated how one bout (1EX) and three bouts (3EX) of strenuous resistance exercise affected the cross-sectional area (CSA) and water content (WC) of the quadriceps muscle and patella tendon (PT), 4 h and 52 h after the last exercise bout. Ten healthy untrained male subjects performed 1EX with one leg and 3EX with the other leg. CSA and WC were measured with magnetic resonance imaging 10, 20 and 30 cm proximal to the tibia plateau (TP) for the muscle, and at the proximal, central and distal site for the PT prior to exercise, and 4 h and 52 h after the last exercise bout. Ten centimeter above the TP, muscle CSA was significantly increased at 4 h (1EX: 13 ± 5%; 3EX: 13 ± 4%) and 52 h (1EX: 16 ± 5%; 3EX: 16 ± 5%) compared with baseline. Muscle WC was significantly increased at 4 h (1EX: 7 ± 1%; 3EX: 6 ± 2%) and 52 h (1EX: 8 ± 2%; 3EX: 8 ± 3%) compared to baseline. PT central CSA was significantly reduced at 52 h (3EX: 14 ± 2%) compared with baseline and (3EX: 13 ± 1%) compared with 4 h. Present data demonstrate that strenuous resistance exercise results in an acute increase in muscle WC and underlines the importance of ensuring sufficient time between the last exercise bout and the determination of anatomical dimensions in muscles.

Effects of vitamin D supplementation on body fat accumulation, inflammation, and metabolic risk factors in obese adults with low vitamin D levels - results from a randomized trial

BACKGROUND

Low plasma 25-hydroxy-vitamin D (25OHD) is associated with obesity. Vitamin D (VD) may be implicated in obesity and its complications such as insulin resistance, hypertension, and low-grade inflammation. We investigated the effects of VD supplementation on fat distribution and on obesity complications in obese adults with low plasma levels of 25OHD.

METHODS

In a double-blind design 52 subjects aged 18 to 50years with BMI>30kg/m(2) and plasma 25OHD <50nmol/l were randomized to 26weeks of treatment with 7000IU of VD daily or placebo. Body composition was assessed by DXA and subcutaneous (SAT) and visceral adipose tissue (VAT), intrahepatic (IHL) and intramyocellular lipids (IMCL) were evaluated by magnetic resonance imaging and magnetic resonance spectroscopy. Insulin resistance (HOMA-IR), blood pressure, plasma lipids, and circulating inflammatory markers were also investigated.

RESULTS

VD treatment increased mean plasma levels of 25OHD from 33nmol/l to 110nmol/l (P<0.0001) and decreased median parathyroid hormone levels from 5.3 to 4.5pmol/l (P<0.01) in the intervention group. Treatment did not change body fat, SAT, VAT, IHL, or IMCL compared with placebo. Neither did treatment affect HOMA, blood pressure, plasma lipids or any of several inflammatory markers investigated including hsCRP.

CONCLUSION

Increasing 25OHD levels by VD treatment for 26weeks have no effects on obesity complications in obese adults with low baseline plasma 25OHD.

Whole body metabolic effects of prolonged endurance training in combination with erythropoietin treatment in humans: a randomized placebo controlled trial

Erythropoietin (Epo) administration improves aerobic exercise capacity and insulin sensitivity in renal patients and also increases resting energy expenditure (REE). Similar effects are observed in response to endurance training. The aim was to compare the effects of endurance training with erythropoiesis-stimulating agent (ESA) treatment in healthy humans. Thirty-six healthy untrained men were randomized to 10 wk of either: 1) placebo (n = 9), 2) ESA (n = 9), 3) endurance training (n = 10), or 4) ESA and endurance training (n = 8). In a single-blinded design, ESA/placebo was injected one time weekly. Training consisted of biking for 1 h at 65% of wattmax three times per week. Measurements performed before and after the intervention were as follows: body composition, maximal oxygen uptake, insulin sensitivity, REE, and palmitate turnover. Uncoupling protein 2 (UCP2) mRNA levels were assessed in skeletal muscle. Fat mass decreased after training (P = 0.003), whereas ESA induced a small but significant increase in intrahepatic fat (P = 0.025). Serum free fatty acid (FFA) levels and palmitate turnover decreased significantly in response to training, whereas the opposite pattern was found after ESA. REE corrected for lean body mass increased in response to ESA and training, and muscle UCP2 mRNA levels increased after ESA (P = 0.035). Insulin sensitivity increased only after training (P = 0.011).

IN CONCLUSION

1) insulin sensitivity is not improved after ESA treatment despite improved exercise capacity, 2) the calorigenic effects of ESA may be related to increased UCP2 gene expression in skeletal muscle, and 3) training and ESA exert opposite effects on lipolysis under basal conditions, increased FFA levels and liver fat fraction was observed after ESA treatment.

Controlled longitudinal bone growth by temporary tension band plating

Permanent growth arrest of the longer bone is an option in the treatment of minor leg-length discrepancies. The use of a tension band plating technique to produce a temporary epiphysiodesis is appealing as it avoids the need for accurate timing of the procedure in relation to remaining growth. We performed an animal study to establish if control of growth in a long bone is possible with tension band plating. Animals (pigs) were randomised to temporary epiphysiodesis on either the right or left tibia. Implants were removed after ten weeks. Both tibiae were examined using MRI at baseline, and after ten and 15 weeks. The median interphyseal distance was significantly shorter on the treated tibiae after both ten weeks (p = 0.04) and 15 weeks (p = 0.04). On T1-weighted images the metaphyseal water content was significantly reduced after ten weeks on the treated side (p = 0.04) but returned to values comparable with the untreated side at 15 weeks (p = 0.14). Return of growth was observed in all animals after removal of implants.

Temporary epiphysiodesis can be obtained using tension band plating. The technique is not yet in common clinical practice but might avoid the need for the accurate timing of epiphysiodesis.

Cite this article: Bone Joint J 2013;95-B:855–60.

High-dose resveratrol supplementation in obese men: an investigator-initiated, randomized, placebo-controlled clinical trial of substrate metabolism, insulin sensitivity, and body composition

Obesity, diabetes, hypertension, and hyperlipidemia constitute risk factors for morbidity and premature mortality. Based on animal and in vitro studies, resveratrol reverts these risk factors via stimulation of silent mating type information regulation 2 homolog 1 (SIRT1), but data in human subjects are scarce. The objective of this study was to examine the metabolic effects of high-dose resveratrol in obese human subjects. In a randomized, placebo-controlled, double-blinded, and parallel-group design, 24 obese but otherwise healthy men were randomly assigned to 4 weeks of resveratrol or placebo treatment. Extensive metabolic examinations including assessment of glucose turnover and insulin sensitivity (hyperinsulinemic euglycemic clamp) were performed before and after the treatment. Insulin sensitivity, the primary outcome measure, deteriorated insignificantly in both groups. Endogenous glucose production and the turnover and oxidation rates of glucose remained unchanged. Resveratrol supplementation also had no effect on blood pressure; resting energy expenditure; oxidation rates of lipid; ectopic or visceral fat content; or inflammatory and metabolic biomarkers. The lack of effect disagrees with persuasive data obtained from rodent models and raises doubt about the justification of resveratrol as a human nutritional supplement in metabolic disorders.